I often see cracks in garage floors; heck, I even have some in my own garage. Most people assume they aren’t a problem, but that’s not always the case.
I recently previewed a home for clients that had a giant crack running from one side of the garage to the other. Outside, the crack ran up the foundation and disappeared under the siding. (I had seen a similar crack in a brick sided home before and the brick on the garage wall had all started to sag, in that familiar step-down pattern that shows structural problems. A bit of research on that one and I had discovered it was a serious problem — the garage was attached to the rest of the house and if the foundation is sagging, it can take the rest of the house with it.)
Anyway, I contacted the listing agent of the home I’d previewed to see if he knew anything about the crack — it was obvious that someone had tried to parge it, but that didn’t work, the crack had expanded. And he said not to worry, a garage floor isn’t structural, it’s like a basement floor with a crack in it.
But I knew that wasn’t correct. So I went back and did more research to refresh my memory. And sure enough, what I had seen was a sign of structural damage according to this website:
Another serious concern suggested by a floor slab crack can be inferred if if the floor cracks track to corresponding cracks in the building foundation wall. If you follow a basement or slab floor crack across the surface to the foundation wall, and if you find a crack in the foundation wall which maps onto the wall from the end of the floor crack, there is risk of more serious foundation damage and further investigation by an expert is warranted.
From what I’ve read, it can be an expensive fix so well worth being cautious. Sometimes the cracks can be “mud-jacked” which means injecting concrete into the holes and spaces beneath the crack where the ground has shifted or dropped away. But it can also require breaking up and re-pouring the entire concrete floor. And in some instances, you have to lift up the entire garage to do that.
So my advice is don’t assume that a garage floor crack doesn’t mean anything, and don’t assume that your realtor is an expert if they tell you it isn’t significant. If one side of the concrete is higher beside the crack than the other, it can be a sign of serious heaving. Anything over the width of two nickels is well worth investigating. This is one of those situations where I wouldn’t rely strictly on my home inspector, either; I’d bring in someone who knows concrete/foundations. In Ottawa, I’d call Steve and Chris at Ardel Concrete Foundations – they’re the best.